(1) Field of the Invention
The present invention relates to a sintered silicon nitride body having a novel composition, which is improved in mechanical properties such as creep resistance and flexural strength at high temperatures and is excellent in the oxidation resistance.
(2) Description of the Prior Art
A sintered silicon nitride (Si.sub.3 N.sub.4) body is known as a high temperature material or a high abrasion resistance material. However, Si.sub.3 N.sub.4 is defective in that the sintering property is bad, and as a material for production of a sintered body having high density and high strength, there has already proposed a silicon nitride composition in which an oxide of an element of the group IIIa of the Periodic Table, such as yttria (Y.sub.2 O.sub.3), is incorporated or Al.sub.2 O.sub.3 is further incorporated (see, for example, Japanese Patent Publication No. 21091/74 or No. 3649/77). However, a sintered body obtained from this composition is still insufficient in the flexural strength at room temperature (about 60 kg/mm.sup.2), and it has been found that when this sintered body is used for a long time at a high temperature, especially in a high-temperature oxidative atmosphere, the sintered body readily undergoes oxidation and such characteristics as the creep resistance, flexural strength, dimension precision and shape precision are drastically reduced.